Posted
by
timothy
on Friday December 05, 2008 @09:00AM
from the bouncy-bouncy dept.

Ponca City, We love you writes "Powerful telescopes in Hawaii and Spain are using 'light echoes' from the original supernova explosion that have bounced off dust in the surrounding interstellar clouds to identify the precise type of supernova that Tycho Brahe saw 436 years ago. Although the echoed light from Tycho's supernova is around 20 billion times fainter than the original light observed in 1572, the team took identical images of the sky a few months apart and then digitally subtracted one from the other to find evidence for several sets of light echoes rippling across patches of dust in the northern Milky Way. 'Using light echoes in supernova remnants is time-travelling in a way, in that it allows us to go back hundreds of years to observe the first light from a supernova event. We got to relive a significant historical moment and see it as the famed astronomer Tycho Brahe did hundreds of years ago,' said Tomonori Usuda, of the Subaru Telescope in Hawaii. Tycho's original observations were particularly important as he immediately concluded that the new star, visible even by day, could not be closer than the Moon challenging the Aristotelian view of the cosmos, widely accepted since ancient times, which held that the sky beyond the Moon never changed."

In human experience, a reflection is instantaneous, where an echo appears after a period of time. Thus echo is more descriptive to layman (remember them?). You know and I know that a reflection isn't instantaneous, it's just not generally perceptible to our eyes like an echo is perceptible to our ears.

...continues to bring surprises like this. I'm just wondering if this is the same method we astronomers use to detect local masses such as transneptunian planets (or "Plutoids", if you will) or asteroids or -gulp!- Near Earth Objects such as the Saturn V Stage discovered and misidentified as a natural coorbiting body a couple years ago? Could light ripples be detected and identified on a pair of plates of the same patch of sky taken a year apart?

This could be used to determine distances very precisely. If we know when that light was emitted and we know the speed of light, then we can calculate with great precision the distance from the star to the reflecting dust cloud.

You also have to account for any differences between the earth-star distance and the earth-cloud distance, but it's still the largest ever radar system.

True. Actually, the real difference between the meaning of the word "reflection" and "echo" lies on in the delay but in the repeat. An echo is a reflection that is perceiving after one has already perceived the same thing the first time. So, although you see the gun fire and a second later here the report, that first hearing of the report is not an echo. But when you then hear the same report reflected off of the wall behind the guy firing the starting pistol, that is an echo. Since we saw the original supernova, then saw the reflection after, the second perception is of an echo. The delay is less important to the distinction than the fact that it's a repeat.

all these high powered telescopes that can 'supposely' see 10000000000x millions of light years away and yet there are no close up's of the moon, the flag on the moon, the machines left on the moon or any other human impact images of the moon from multiple sources across the world. No images exist except those from the 1969.

It's not just computing power. We'd actually need to catch enough reflected photons that originated from the Earth, so we'd have anything at all to process.

I think it would be a problem even if there was no other light except what we want to observe, ie. there would be no external noise.

Also, the "mirror" isn't a flat plane, so we'd get a bunch of "Earth photons" that originatead at different times, reflected at different times, and then arrive at our telescope at the same time.

To get anything useful, we'd need to have a very sharp focus, and then move the focus at the speed of light, so we'd collect photons that originated at the same time, but reflected at different times.

So sharpness of focus would determine temporal resolution. If we'd want to catch an apple falling, we'd need temporal resolution of maybe 1/10th of a second (and that would still be quite a blurr), so focus would have to be 1/10th of a light second... I don't know that much about optics, but achieving that at a distance of hundreds of light years would be quite a feat too... Will a telescope array help with achieving a sharp focus at a great distance?

It is laudable, but I wonder how much doubt there was going on at the time. For instance, the Greeks knew that the Earth was round, but there was common conception that the Earth was flat -- I'm not talking about what educated people thought, but what the commoners thought. European scholars studied classical literature ( back then it was just "literature" I guess ), and they were exposed to ideas from the Greeks and the Muslims, who helped transmit the Greek texts. So they got exposed to a lot of different ideas.

The official line of the church was that the heavens never changed and were perfect, and if you wanted to be in the good graces of the church, which was a good idea to a lot of people, they towed the line. Of course, to the common person, the sky was a round dome, because that's what it looks like, and that's what the priest tells him. But I think that the educated class might have been more open-minded.

Anywho I have a friend who claims that our perception of the universe is wrong -- we're basically looking at a big optical illusion that also affects gravity somehow. He doesn't claim to know what it should really look like, but he says what we are seeing is an optical illusion. I can kinda see his point -- all the instruments we have are earth based, and if there's some uniform membrane or something around the solar system, how could we tell? I don't know enough to prove him wrong, so whatever.